The present invention relates to fuel injectors for delivery of fuel to the intake system of an internal combustion engine and, more particularly, to an electromagnetic fuel injector having a disk-shaped armature.
Inclusion of a disk-shaped instead of a cylindrical armature in an electromagnetic fuel injector provides important advantages, including compactness, a substantial reduction in the mass of the armature, greatly diminished sliding friction during operation of the injector, and a consequent reduction in wear. Use of a disk-shaped armature, however, also presents some problems. During operation of the injector, the armature must be relatively precisely positioned as it contacts the valve seat in order to sufficiently prevent or control the flow of fuel to the combustion chamber. In operation, the armature is urged toward the valve seat by a return spring. The spring acts on a relatively small surface area of the armature. The return spring force is often not uniform on the surface. Uneven spring forces may tilt or tip the armature or otherwise fail to properly seat the armature on its valve seat. A conventional disk-shaped armature has a tendency to tip as it returns to its closed position, resulting in improper valve seating and undesirable fuel leakage. In the past, disk-shaped armatures have been treated with a lubricious coating to reduce friction and binding so as to encourage proper seating alignment. Coating of the armature, which requires additional processing steps, adds to the manufacturing costs of the armature. Also, in the prior art, in order to encourage proper seating alignment, disk-shaped armatures have been hinged to the mating seat. The hinged design requires precise assembly techniques which again adds to the manufacturing costs. Thus, there is a continuing need for a fuel injector comprising a disk-shaped armature that is reliably returned to a proper alignment with a valve seat during operation of the injector. Also, what is needed in the art is a reliable and inexpensive way of accomplishing this. These needs are addressed by the present invention.
The present invention is directed to an electromagnetic fuel injector having a disk-shaped armature that is biased in the closing direction by a ring-shaped flexible element and maintains a degree of lateral and rotational freedom to reliably seat itself when biased closed. The fuel injector of the present invention comprises a body having a fuel inlet and a fuel outlet and a base having a valve seat. A disk-shaped armature is disposed at the fuel outlet for controlling the flow of fuel. The armature has an upper surface and a lower surface that comprises a sealing interface with the valve seat. A flexible element comprising a ring, and at least one flexible leg projecting from the ring is in contact with the injector body and the upper surface of the armature and provides a spring bias between the body and armature upper surface. When the injector is closed, a spring bias from the return spring and the flexure act on the armature upper surface to maintain the armature in a sealing position with the valve seat, while permitting a degree of lateral and rotational freedom for the armature to be positioned flatly on the seat. When the injector is open, the return spring is compressed and the flexure is bent. With the injector open, there is an increase in spring bias between the body and armature upper surface to impel the armature to return to a sealing position with the valve seat when the solenoid is de-energized.
By disposing the flexures on the outer annular surface of the armature, the combined bias forces of the spring and the flexures are more stable and reliable in seating the armature than a spring only embodiment. The flexure forces provide a seating force on the outside of the armature to balance the central seating force of the return spring. With the invention, spring seating forces act on both the central surface portion of the armature and outer peripheral annular portions of the armature. Thus, the seating force is distributed across the surface of the armature and is not concentrated directly above the valve seat. By distributing the seating forces across the upper face of the armature, the invention more reliably seats the armature on the valve seat.
The flexures also provide radial inward forces that urge the armature to a centered position over the valve seat. As such, the flexures provide some radial restraint to resist lateral displacement of the armature during its travel from its open to its closed position on the valve seat. The invention does not require the hinges used by conventional injectors. Instead, the invention relies on the radial bias forces of the flexures to generally center the armature without connecting the armature to the valve seat.
An advantage of the present invention is that an inexpensive, reliable disk-shaped armature can be used in an electromagnetic fuel injector without the need for coating the armature or hinging the armature to assure proper seating.
Another advantage of the present invention is that some traditional, costly, precision assembly techniques need not be used to manufacture the fuel injector.
A further advantage of the present invention is that the disk-shaped armature is positively urged to return to a proper alignment with its valve seat during operation of the injector.